A variety of devices are known for translating bodily movements of one kind or another into variations in electrical signals or parameters. The most common of these are manually-operated rotary and linear potentiometers, manipulated by the hand(s) of the operator. While this is in many cases satisfactory, in some instances the hands of the operator are unavailable for these tasks, as in the case of a musician, both of whose hands may be occupied in the manipulation of an instrument. To circumvent this problem, control devices have been mounted in pedals for manipulation by the feet. This often proves clumsy in practice, as foot dexterity in most persons is less developed than manual dexterity. There are also instances where both the hands and the feet of the operator are unavailable, as in the case of musicians playing instruments which require both hand and foot operation, the case of disabled persons who have lost the use of hands and feet, and the case of persons operating complex machinery requiring the use of hands and feet.
There exist in the art several devices which sense eye movements and/or blinking. U.S. Pat. No. 3,379,885 by C. L. Nork and U.S. Pat. No. 4,081,623 by A. W. Vogeley illustrate two such devices. These are generally awkward and obtrusive in use, requiring a head-mounted apparatus aimed at the eye(s). They are often binary in nature, generating only pulse-type signals indicating only that an eye movement has or has not occurred. Furthermore, they are relatively costly, precluding their use in general, consumer-oriented products.
Several types of mouth-operated devices are also in common use, particularly in the field of electronic musical instrument control. One type requires the operator to blow or suck on a hollow tube, causing a flow of air or a pressure variation which is sensed electronically. Another type requires the operator to "bite", with varying intensity, on a pressure-sensitive device. These mouth-operated devices overcome the limitations of the manual, pedal, and ocular devices previously mentioned, but all involve relatively expensive and/or "exotic" technology. In certain cases, particularly the control of resonant filters in spectral shaping of electronic musical instruments, their particular mode of operation may lack "naturalness", due to a lack of correspondence between the mouth movements of the operator and the resultant "vocal" qualities of the filtered instrument.
Control by spoken sounds is also well-known, however, simple, inexpensive sound-operated devices are generally limited to binary, on-off type operation. More elaborate speech-operated devices are available in the form of computerized speech-recognition systems which can distinguish between various spoken words, but these are costly, problematic in high-noise environments, and provide discontinuous control functions, i.e. separate on-off outputs for each recognized utterance. Another type of voice-activated controller is the vocoder, which can superimpose the spectral weighting of spoken utterances onto an instrument's sound. Vocoders are well-suited to tonal modification of electronc musical instruments, but are complex and costly, and are not general-purpose control devices.